1. Field of the Invention
The present invention relates to polyester laminates, for example, release base materials and base material for paper containers having excellent heat stability and mechanical strength which are prepared by using aliphatic polyesters with biodegradability and sufficiently high molecular weights and specific melt properties for practical use.
2. Discussion of the Background
As a release base material, one comprising a release layer laminated on a filling layer on one or both sides of a paper or a cloth has been well known, wherein said filling layer is a low density polyethylene having a long branched chain obtained by the ordinary high-pressure method, a medium density polyethylene obtained by blending a low density polyethylene with a high density polyethylene, or a composition obtained by blending a low density polyethylene with polypropylene.
Further, as for paper cups such as used for foods and drinks, for example, coffee, soup, miso-soup and instant noodles, paper trays for food, for example, pizza, daily dishes and food for microwave ovens and the like, at least inner surface where the content such as liquid contacts, a resin composition as same as aforementioned is conventionally laminated to provide a water-repellent layer.
In the current processes for producing the release base materials, it is required to melt-coat the polyolefins used as a filling layer as mentioned above on base materials at a high temperature over 315.degree. C. in order to obtain close-adhesive and bonding properties between the polyolefins and the base materials.
Further, in the production of the base material for paper containers used for hot drinks and foods such as paper cups or paper trays, it is required to laminate the above-mentioned polyolefin compositions used as a water-repellent layer on the paper at a high temperature over 300.degree. C. in order to coat the polyolefin composition firm to the paper.
Because of this high temperature melt-coating, the oxidative deterioration of the polyolefin themselves occurs, and the generation of a great volume of smoke is unavoidable. Consequently, not only is the condition of the working environment worsened, but also the living environment around the factory becomes polluted by the smoke exhausted from the factory, creating a great community problem. Accordingly, there has been a strong demand for improvement thereof. On the other hand, waste disposal of the used release papers by burying them in the earth is insufficient, since the base materials are laminated with unbiodegradable polyolefins. Furthermore, trying to recycle the paper from the used release papers, by soaking the paper in an alkaline aqueous solution followed by tearing off the polyolefins, is very difficult and required much labor and cost. Accordingly, there has also been a strong demand for development of a release base material which can be biodegraded together with other biodegradable base materials such as paper and cloth.
One object of the present invention is to develop a release base material filled with a polymer which can be molded at a low temperature in order to minimize the volume of generated smoke in the melt-coating process, which has good bonding and firm-adhesive properties to the base material such as paper and cloth and which can be decomposed by natural and ordinary microorganisms in the earth.
Another object of the present invention is to develop a novel base material for a paper-made container, by which the problems concerning the odor of the oxidatively deteriorated polyolefin remaining on the paper-made container because of the high temperature lamination and the generation of a great volume of smoke can be solved, and which gives the paper-made container biodegradability and is advantageous to the preservation of the natural environment, where undecomposable materials of the used container have been accumulated.